Coating process for regenerated cellulose foils



COATHN'G PROCESS FDR REGENERATED CELLULOSE FOILS No Drawing. ApplicationMarch 30, 1955, Serial No. 498,108

Claims priority, application Germany March 31, 1954 12 Claims. (Cl.117-144) The present if'ivention relates to foils of regeneratedcellulose provided with a coating for the purpose of improving the foilsfastness to moisture as well as its tightness to gases. Moreparticularly the invention relates to a process of enhancing theadhesion of the coating to the surface of the foil of regeneratedcellulose by a chemical treatment of the foil before coating it.

In order to produce so-called moisture-proof foils of regeneratedcellulose, also called moisture-proof cellulose hydrate foils, theregenerated cellulose foils are coated with a moisture-proofingwater-repellent film. Preferably such coatings are used that havehot-sealing properties. Usually the foil is impregnated with a socalledanchoring agent before being coated for the purpose of increasing theadhesion of the coating to the foil. As a further advantage of usingsaid anchoring agent the coating does not peel ofi. from the base foileven when the moisture-proofed foil is exposed for a longer period oftime to the influence of water or wet substances.

Principally, there are two possibilities of impregnating the foil withthe anchoring agent:

(a) In connection with the production proceedings and before it entersthe drying chamber, the foil is passed through a bath in which theanchoring agent is dissolved.

ttes Patent Usually, the anchoring agent is added to the bath containingthe softening agent, e. g. glycerol.

(b) Or the finished foil, i. e. the dried and rolled up foil, isimpregnated by a separate dipping or spraying operation with thesolution of the anchoring agent, and subsequently dried.

By coating foils thus provided with an anchoring agent moisture-proofcellulose hydrate foils are obtained which are especially suited forpackaging either wet goods, such as jam, meat etc; which must beprevented as far as possible from losing moisture, or substancesdetrimentally affected by moisture which must be protected against theinfluence of atmospheric dampness or condensed humidity.

Almost all of the anchoring agents hitherto known are suited only forthe second method sub (b), in which the treatment of t foil with theanchoring agent is a separate process step and which is therefore moreex pensive and more troublesome than the other method, for whichsuitable anchoring agents have been lacking so far.

The present invention is concerned with a process for producing coatedregenerated cellulose foils according to which process the foils can beimpregnated with the anchoring agent in a satisfactory degree alsoduring their production, before drying. The process is characterized inthat the cellulose hydrate foils are impregnated with anchoring agentswhich are water-soluble reaction products selected from the groupconsisting of reaction products of phosphorous oxychloride (POCls) andalkylene imines and reaction products of phosphorous thiochloride(PSCls) and alkylene imines. For the produc- 2,784,116 Patented Mar. 5,1957- tion of the reaction products to be used according to the presentinvention as anchoring agents there may be also used mixtures ofalkylene imines with secondary aliphatic amines,'such as dimethyl amineand diethyl amine, with the alkylene imine component predominating insaid mixture; advantageously the quantity of alkylene imine should betwice or more that of secondary amine.

The anchoring agents to be used according to the present invention maybe monomeric reaction products of the components in question, or theymay be low degree polymerisation products that are still water-soluble.The monomeric reaction products may be prepared for instance by reactingphosphorous oxychloride or phosphorous thiochloride with alkyleneimines, such as ethylene imine, in the presence of acid-binding agents.In this reaction, instead of using pure alkylene imine, part of saidalkylene imine may be substituted by secondary aliphatic amines, such asdimethyl amine or diethyl amine, thus producingcompounds which maycontain, for instance, 1 mol secondary aliphatic amine and 2 molesalkylene imine for each phosphorus atom present. The reaction issuitably performed while using solvents as reaction medium. Suitablesolvents are aliphatic or aromatic hydrocarbons, or chlorinatedhydrocarbons, such as for instance chloroform, benzene,-toluene,chlorobenzene and similar solvents. Tertiary amines, such as trimethylamine or triethyl amine, and especially anhydrous ammonia, may be usedas acid-binding agents. By the application of mild polymerisationconditions, the monomeric reaction products thus obtained can bepolymerised to such a degree as to be still water-soluble.v

Such polymerisation may be brought about, for instance, by heating to ahigher temperature, up to C. The length of the heating period dependsupon the desired degree of polymerisation. When lower temperatures areapplied, the reaction will take a longer time. Or polymerisation may bebrought about by means of catalysts. Suitable catalysts may be, forinstance: (a) acid catalysts, such as sulfuric acids, sulfurous acid, orcarbonic acid;

(b) dialkyl sulfates, such as dimethyl sulfate, diethyl sulfate,dipropyl sulfate or dibutyl sulfate; (0) p-toluenesulfonic acid alkylesters, such as the methyl and the ethyl ester, and similar compounds;(d) water and other 7 catalysts. Solvents may or may not be used in thepoly v merisation process.

benzene, toluene or xylene are suitably used as solvents.

Aromatic hydrocarbons, such as The polymerisation process can be easilywatchedby taking samples of the reaction mixture or by makingwater-solubility or viscosity tests. If necessary, the polymericcompounds may be separated fromthe monomeric compounds still present byadding suitable diluents. Such diluents may be, for instance, aromatichydrocarbons, such as benzene or toluene, or ketones, such as acetoneetc. Upon adding the diluent to the reaction mixture, the polymerisationproduct precipitates in the form of a solid, white substance. Variousmethods for preparing such compounds are specifically described on pages210-232 in Liebigs Annalen der Chemie, vol. 566 (1950), by HerbertBestian.

discussed on page 215. Such methods are also disclosed in German PatentsNo. 863,055, dated January 15, 1953,

and No. 888,853, dated September 7, 1953.

In order to obtain the desired degree of impregnation" of theregenerated cellulose foil the reaction products according to thepresent invention can be used individually or said reaction products canbe applied in mixture with each other.

The impregnation of the cellulose hydrate foils is ad- The particularlyrelevant" disclosures are to be found onpages 231 and 232, whichdescribe the preparation of compounds XIII and XIV ta thiochloride andalkylene imines to one of the usual aqueous baths through which the foilband passes in p the course of its production, for instance to the bathcontaining the softening agent, Equallygood results are obtained whenthe foil, after. it is dried, is impregnated with the anchoring agent bypassing the dry foil through a solution of the reaction product inorganic solvents. Ethyl alcohol and methyl alcohol are very well suitedas solvents for the anchoring agent. I

Frequently, the impregnating effect of the anchoring agent may beincreased by adding to the impregnating bath acids acting as catalysts.Such acids may be, for instance, boric acid, lactic acid, glycolic acid,citric acid, gallic acid, succinic acid or maleic acid, or a saltshowing acid reaction in aqueous solution may be used, such asmonosodium phosphate or monokaliurn phthalate. Or the foil may besubmitted to a treatment with an acid or an acid reacting salt after ithas been coated with the reaction products of phosphorous oxychloride orphosphorous thiochloride respectively, and alkylene imines. Care must betaken that the solution containing the acid catalyst is not removed bythe impregnating solution if the catalyst is applied before impregnatingthe foil, or, vice verse, that it does not decrease the alreadyestablished impregnation effect, in case that the acid catalyst isapplied after impregnating the foil. In the first case, it is advisableto spray the impregnating: solution of the anchoring agent upon the foilafter it has been treated with the acid catalyst in a dipping bath; inthe latter case, it is advantageous to spray a solution of the catalyston the foil after it has been steeped in the impregnating bath.

Another method of anchoring the coating to the base foil is by addingthe anchoring agent of the present invention to the coating composition.effect thus obtained may be further increased by treating the foil witha solution of an acid catalyst before it is coated. For this purpose,the acid catalyst is suitably added to the softening bath.

The following examples are inserted in order to illustrate the presentinvention without an intention of limiting the invention to what isstated in the examples.

Examples (1) After the usual treatment in the wet section of a spinningor casting machine, a cellulose foil produced by regeneration fromviscose or a cuprammonium solution is passed through a softening bathconsisting of an aqueous solution containing 6% glycerol and 0.2% of areaction product of phosphorous oxychloride and ethylene imine, saidreaction product having undergone some polymerisation. The impregnatedfoil is dried and rolled up. It is then coated with a known coatingcomposition which may, for instance, contain:

dissolved in a 1:1 mixture of acetic ester and benzene.

After drying the coated foil is moisture-proof andthe' coating does notpeel off from the foil even after several months storage under water.

The anchoring (2) The procedure described in Example 1' is followed.

The softening bath consists of water in which are dissolved 8% ofethylene glycol and 0.2% of a reaction product of phosphorousthiochloride and ethylene imine'.

The foil is coated according to the method described in Example 1. Themoisture-proofed foil is resistant to water for several months and mayeven be heated to boiling-without the coating peeling oif.

1(3) The method described in Example 1 is followed.

i The softening bath consists of water containing 8% i ethylene glycoland 0.2% of the reaction mixture of 1 mol phosphorous oxychloride, 1 moldiethyl amine, and 2 moles of ethylene imine. The moisture-proofed foilis also excellently water-resistant and boil-fast.

(4) A dried regenerated cellulose foil made according to the viscoseprocess or the cupramrnonium process is passed through an ethyl alcohol(96%) bath containing 0.5% of a mixture consisting of equal parts of are action product of phosphorous oxychloride and ethylene imine, saidreaction product having undergone some polymerisation, and a monomericreaction product of phosphorous thiochloride and ethylene imine. Afterdrying the impregnated foil is coated with a coating compositioncorresponding to the one described in Example 1. The moisture-proofregenerated cellulose foil thus produced is water-resistant andboil-fast.

(5) Using a softening bath which contains 6% of ethylene glycol, 0.2% ofa reaction product of phosphorous oxychloride and ethylene imine, thereaction product having suffered some polymerisation, and 0.05% ofgallic acid dissolved in water, a cellulose hydrate foil is impregnatedand coatedas described in Example 1. The moisture-proof cellulosehydrate foil thus obtained is excellently resistant to cold and boilingwater.

(6) A regenerated cellulose foil is passed through a softening bathcontaining 6% of glycerol and 0.1% of glycolic acid dissolved in water.After drying, the foil is coated with a coating composition comprisingin addition to the components stated in Example 1 0.5 part by weight ofa reaction product of phosphorous oxychloride and ethylene imine. Thefoil thus coated is water-resistant and boil-fast.

What We claim is:

l. The process of coating a foil of regenerated cellulose comprising theimpregnation of the foil with a watersoluble reaction product selectedfrom the group consisting of reaction products of phosphorousoxychlorideand alkylene imines and reaction products of phosphorous thiochlorideand alkylene imines before the foil is coated.

2. The process described in claim 1 wherein the impregnation of the foilwith said water-soluble reaction product is obtained by adding saidreaction product to an aqueous treating bath.

3. The process described in claim 2 wherein said water-soluble reactionproduct for the impregnation of the foil is added to the bath containingthe softening agent.

4. The process described in claim 1 wherein the impregnation of the foilwith said water-soluble reaction product is practiced after theregenerated foil is dried and before it is coated.

5. The process described in claim 1 wherein said water-soluble reactionproduct contains as an admixture a water-soluble reaction productselected from the group consisting of reaction products of phosphorousoxychloride and secondary aliphatic amines and reaction products ofphosphorous thiochloride and secondary aliphatic amines.

6. The process of coating a foil of regenerated cellulose comprising theimpregnation of the foil with a watersoluble reaction product selectedfrom the group consisting of reaction products of phosphorousoxychloride and alkylene imines and reaction products of phosphorousthiochloride and alkylene imines in the presence of'an acid substanceselected from the group consisting of acids and salts showing an acidreaction in aqueous solution, said impregnation being effected beforethe foil is coated.

7. The process described in claim 6 wherein said acid substance is awater-soluble organic acid.

8. The process described in claim 6 wherein the foil is treated withsaid acid substance before said impregnation with said water-solublereaction product takes place.

9. The process described in claim 6 wherein the foil is treated withsaid acid substance after said impregnation with said water solublereaction product has taken tri-place and before the foilis coated.

h la.)

10. The process of coating a foil of regenerated cellulose wherein acoating preparation is used containing as a component of the mixture awater-soluble reaction product selected from the group consisting ofreaction products of phosporous oxychloride and alkylene imines andreaction products of phosphorous thiochloride and alkylene imines.

11. The process described in claim 10 wherein said water-solublereaction product contains :as an admixture a water-soluble reactionproduct selected from the group consisting of reaction products ofphosphorous oxychloride and secondary aliphatic amines and reactionproducts of phosphorous thiochloride and secondary aliphatic amines.

12. The process described in claim 10 wherein a foil of regeneratedcellulose is coated which has been treated before the coating operationwith an acid substance selected from the group consisting of acids andsalts showing an acid reaction in aqueous solution.

References Cited in the file of this patent UNITED STATES PATENTS1,857,163 Platt May 10, 1932 2,606,900 Parker Aug. 12, 1952 2,654,738Lecher Oct. 8, 1953 2,698,793 IJandes Ian. 4, 1955

6. THE PROCESS OF COATING A FOIL OF REGENERATED CELLULOSE COMPRISING THEIMPREGNATION OF THE FOIL WITH A WATERSOLUBLE REACTION PRODUCT SELECTEDFROM THE GROUP CONSISTING OF REACTION PRODUCTS OF PHOSPHOROUSOXYCHLORIDE AND ALKYLENE IMINES AND REACTION PRODUCTS OF PHOSPHOROUSTHIOCHLORIDE AND ALKYLENE IMINES IN THE PRESENCE OF AN ACID SUBSTANCESELECTED FROM THE GROUP CONSISTING OF ACIDS AND SALTS SHOWING AN ACIDREACTION IN AQUEOUS SOLUTION, SAID IMPREGNATION BEING EFFECTED BEFORETHE FOIL IS COATED.